Figure 1.
Multispectral filter arrays (MSFAs) using grayscale lithography with metal–insulator–metal (MIM) geometry. (a) Schematic: (i) using a customized MSFA atop a monochrome image sensor for multispectral imaging. (ii) 3D MIM structure of MSFA with inset detailing layers. The wavelength transmitted to each pixel below the MIM structures is controlled with the single-step lithographic fabrication process. (b) MSFA fabrication process: (i) a spatially varying grayscale exposure dose results in a spatially varying wavelength transmission profile. (ii) Calculated grayscale exposure dose profile corresponding to remaining resist thickness profiles (“resist sensitivity” curve). An ultrathin noble metal (Ag) layer on glass (SiO2) acts both to dissipate accumulated charge and as the bottom mirror of the filter. (iii) A spatially variant dose modulated exposure leaves a 3D resist profile postdevelopment. (iv) Post-metal-deposition: with a top metal (mirror) layer, the spatially varying 3D resist profile acts to filter the light according to the eigenmode solution of the stack. (v) Final spectral transmittance profiles of MIM structures.